The present invention relates to an improved cutting cup for sphere making machines.
It is known in the lapidary art to make spheres of rock and similar materials using a sphere making machine. In making rock spheres, the piece of rock is first cut into a perfect cube. The corners of the cube are then cut off, and then the resulting corners cut off again for a total of 32 cuts. The resulting rough sphere is ground so it is fairly rounded, and then placed into a sphere making machine. Machines for making such spheres have either two or three concave grinding cups that are rotated by spindles to grind against the surface of the rock to create a sphere. The interior of the concave grinding cups typically contains a coating of an abrasive, such as 40/50 mesh diamonds sintered to a cup made of cast iron.
Such sphere making machines are commercially available. A two head “little sphere” machine is available as Covington Model 382, and a two head “large sphere” machine is available as Covington Model 381. A three head sphere machine is available as Covington Model 383.
With the conventional grinding cups currently commercially available it typically takes 4–6 hours to form a rock sphere.